One of the most important proteins in energy transduction is the ATP-Synthase (FOF1). This membrane- bound large protein complex is present in nearly all organisms and is essential for all higher life on earth, including humans. Slight defects in function, assembly and the degradation pathways of the enzyme play important roles in severe diseases such as the Batten's disease, Alzheimer's disease and the Retinitis Pigmentosa Syndrome. Furthermore, human mitochondrial ATP Synthase is highly regulated in response to cellular energy needs. The aim of this project is to unravel the structure and catalytic mechanism of this enzyme. The ATP Synthase functions as a molecular (nano) motor, thereby catalyzing the synthesis of ATP from ADP and Pi driven by a transmembrane electrochemical potential of protons or sodium ions. The enzyme complex consists of two distinct structural and functional domains: A membrane intrinsic proton translocation system (the FO part), which is structurally connected by at least two "stalks" to the membrane extrinsic domain (the F1 part), which in turn harbors the nucleotide binding sites. While several structures of the membrane extrinsic F1 part and individual protein subunits of the ion conduction FO part have been determined by X-ray structure crystallography, the molecular elucidation of the coupling mechanism still suffers from the lack of information on the structure of the complete intact ATP Synthase and the membrane intrinsic proton translocation machinery. The goal of this project is to determine the structure of proton turbine of the ATP-Synthase and discover the mechanism of the coupling between proton transfer and ATP-synthesis. The project aims to crystallize the intact ATP Synthase, the proton conducting FO part as well as the c-ring rotor of the enzyme, which differs in its oligomeric state between different organisms. The crystals will be used to determine the structure of the protein complexes by X-ray crystallography. The structural information will form the basis for the discovery of the mechanism of the dynamic energy coupling in the catalytic cycle of the enzyme.